Variable lead device for indicium tracers



Feb. 17, 1970 L. M. LAYDEN 3,496,437

VARIABLE LEAD DEVICE FOR INDICIUM 'I'RACERS Filed April 18, 1966 3 Sheets-Sheet 1 FIG. o

INVENTOR 8V L.M.LAYDEN AGENT 17, .1970 I L. M. LAYDEN 3,

4 VARIABLE LEAD DEVICE FOR INDICIUM TRACERS Filed April 18, 1966 3 Sheets-Sheet 2 F/G.3 I64 I70 a SPEED/ l SELECTOR nz m INVENTOR By L. M. LAVDEN AGENT Feb; 17, 1970 L. M. LAYDEN 3,496,437

VARIABLE LEAD DEVICE FOR INDICIUM TRACERS Filed April 18, 1966 3 Sheets-Sheet 5 FIG. 7'

I68 Pne MOTOR CONTROL l I II I HHIIII ODOMETER I MOTOR v/Nl/E/VTOR By L.M. LAD DEN AGENT United States Patent 3,496,437 VARIABLE LEAD DEVICE FOR INDICIUM TRACERS Lawrence M. Layden, Basking Ridge, N..I., assignor to Air Reduction Company, Incorporated, New York N.Y., a corporation of New York Filed Apr. 18, 1966, Ser. No. 543,337

. Int. Cl. H0211 5/46 US. Cl. 318-18 2 Claims ABSTRACT OF THE DISCLOSURE In apparatus for automatically tracing a pattern a sensing device scans an area in advance of the axis about which the tracing device rotates to follow the pattern. Means are provided for correlating the extent of the lead of the sensing device with the travel speed of the tracing device.

application of the invention is not to be construed as limited thereby. Whenever a line to be traced is referred to herein, it will be understood that the term line is generic to an elongated indicium, whether a line or an edge, and whether the indicium is upon a work surface or upon a template, it being evident that the invention does not depend upon the form of the indicium to be traced.

In tracing systems involving the tracing of curved lines or the turning of corners, there is a certain more or less constant minimum interval of time which the mechanism requires in order to execute any given turn. For this reason, it is generally necessary that the line tracing device be able to look ahead, so to speak, far enough to anticipate the need for a turn, so that the turn can be executed at the required place. The distance measured.

along the line to be traced, which is necessary to insure the required anticipation, is called a lead or lead distance."

In the field of metal cutting equipment which cuts by thermal or therrno-chemical means, it has been found that higher cutting speeds require greater lead distances. For example, with oxy-thermal flame cutting equipment, used at cutting speeds customarily about 3 to 30 inches per minute, a lead distance of about one-sixteenth inch has been used. 'On the other hand, for an electric arc plasma cutting machine, operating in the speed range of .200 to 250 inches per minute, a lead distance of onequarter inch to three-eighths inch may be required.

It will be understood, however, that the invention is applicable to tracing systems generally and is not to be construed as limited to metal cutting equipment.

An object of the invention is to improve the fidelity of aline tracer in following a given line.

, Another object is to achieve a uniform degree of fidelity in the operation of a line tracer over a range of tracing speeds, particularly to maintain the fidelity constant as the tracing speed is increased.

A further object is to avoid swinging wide at corners at the higher tracing speeds, or conversely, exceesive rounding of corners at the lower speeds.

Another object is to avoid unstable operation of a line tracer at any given tracing speed.

Otherwise expressed, a general object is to promote optimum performance of a line tracer at all desired operating speeds.

A particular object is to automatically adjust the lead distance as a function of travel speed.

In accordance with one embodiment of the invention, a scanned area upon the work surface or upon a template forms an optical image upon a sensing device, preferably comprising light-sensitive resistors, by means of a lens supported in an optical spindle. Means such as a lead screw is provided for varying the position of the sensing device with respect to the optical axis of the spindle and lens. By this means the distance between the scanned area and the projection of the optical axis upon the work or template can be adjusted. This distance constitutes the lead in this instance. A motor is provided for driving the lead screw for the purpose of varying the lead. This motor may be controlled by means of a servo link connecting it with the speed control device which controls the travel speed of the machine that comprises the tool and the optical spindle. The servo link is arranged to cause the sensing device to be moved to a particular position related in a predetermined manner to the speed as determined by the speed control device. It will usually be desired to have the lead increase as the travel speed increases and decrease as the travel speed decreases. The relationship between the lead and the the travel speed may be either a linear one or the lead may be some other function of the travel speed.

Alternatively, the screw which determines the lead distance may be mechanically linked with the speed control device which controls the travel speed of the tool and optical spind e. In this case, adjustment of the speed control device will move the Sensing device directly to adjust the lead distance in accordance with the travel speed, without the intermediary of the servo link.

The lead distance as used herein is measured in the plane of the workpiece or of the template. If the magnifi cation of the optical system employed between the workpiece or template and the plane of the sensing device is unity, the displacement of the sensing device from the optical axis as measured in the plane of the sensing device is the same as the lead measured in the plane of the workpiece or template. If the magnification is in a ratio other than one to one, the magnification ratio must be applied in determining how far the sensing device must be moved to effect a given change in the lead as measured in the plane of the workpiece or template.

In some cases, it may suffice to divide travel speeds into discrete ranges and to have the linkage change the lead in discrete steps, as needed, with each said step corresponding to particular range of travel speeds.

Other features, objects and advantages will appear from the following more detai ed description of illustrative embodiments of the invention, which will now be given in conjunction with the accompanying drawings.

In the drawings,

FIGURE 1 is a plan view of a tracer in typical relationship to a surface S bearing an indicium L to be traced, to a fixed member 1, and to a tool T whose guidance may be the ultimate function of the tracing;

FIGURE 2 is an enlarged and more fully developed plan view of the tracer of FIGURE 1;

FIGURE 3 is a vertical cross-sectional view taken along the line 33 of FIGURE 2;

FIGURE 4 is an enlarged vertical cross-sectional view taken along the line 4-4 of FIGURE 2;

FIGURE 5 is a vertical cross-sectional view taken along the line 5-5 of FIGURE 4;

FIGURE 6 is a diagram relating a sensing device as viewed along the line 6-6 in FIGURE 3 to the image of a line when the tracer is in process of tracing the line; and

FIGURE 7 is a fragmentary view, partly sectional and partly diagrammatical, showin an application of the invention to a magnetic type of line tracer.

A typical organization of a tracer in which the invention may be incorporated is shown in FIGURES 1, 2 and 3. Therein 10 designates a carriage which is supported by a single upright traction wheel 30 (see FIG- URE 3) pivoted on both horizontal and vertical axes. The carriage' is freely movable, within limits, in translation in all horizontal directions over a surface S therebeneath on which the traction wheel 30 rests. The carriage is, however, restrained against rotation parallel to that surface, and is restrained against any tilting from parallel to the surface S, in any suitable manner. By way purely of simple schematic illustration of means for exerting these restraints, FIGURE 1 shows a pair of strong and sturdily pivoted pantographic arms 2 pivotally connected to it and to a stationary member 1.

The immediate function intended to be performed by the carriage 10 is its movement over the surface S in a path corresponding to an elongated indicium (eg a line or an edge) appearing on the surface S; the ultimate function is the guidance of a tool (e.g. a metal-cutting torch) coupled to it in some suitable manner, over work to be operated on by that tool, in a path corresponding to that indicium. Thus in the schematic plan of FIGURE 1 the indicium appears as the line L; the tool appears as the torch T, supplied with fuel by the hose H, directed downwardly to propel its flame against work in the form of a plate W and, purely by way of example, coupled to the carriage by the rigid bracket 3 to which it is clamped; and the path to be traversed by the tool over the worki.e., along which the flame projected by the torch will impinge on and cut through the workappears as P, correspondin in configuration to the line L.

The carriage itself may comprise a main rectangular platform 11; a supplemental platform 12, for example generally L-shaped, secured in spaced relation to and above the platform 11; and a member 13 extending upwardly, for example at the righthand end of the platforms 11 and 12.

A mount 20 for the traction wheel 30 is journalled o a vertical axis in the platforms 11 and 12 to provide for the Vertical-axis pivoting of the traction wheel. As best seen in FIGURES 4 and 5, this mount may comprise a relatively thick-walled tube 21 to which are secured one of the races of a ball bearing 23 of which the other race is secured to the platform .11, and one of the races of a ball bearing 24 of which the other race is secured to the platform 12. The bearings 23 and 24 resist upward thrust of the tube 21, which in the absence of that thrust may for example be retained therein by the large circular nut 25 locked on the tube 21 just above the platform 12. At the bottom of the tube 21 there may be secured to it a suitably shaped casting 26 Whose principal portion is a downwardly extending vertical wall 27, more displaced from the axis of the tube than is the wall of the latter and provided near its bottom with a horizontal boss 28 extending toward that axis. The traction wheel 30 may be mounted on a shaft 31 journalled in that boss. Obviously the vertical plane in which the traction wheel is disposed may be swung about the axis of the mount 20 by angular movement of that mount in the bearings 23 and 24; this provides for steering of the carriage.

Propulsion of the carriage, by way of example in the direction indicated by the arrow in FIGURES 3 and 4, is provided for by applying a rotating force about its horizontal axis to the traction wheel 30. This force may be conducted to the traction wheel through a shaft 32 coaxial with the tube 21 and journalled therewithin in suitable bearings of which the lower one only is shown as 33; this shaft may extend downwardly to a little above the traction wheel, and may there carry a worm 34. At the level of the worm the wall 27 may be provided with another horizontal boss 29, and in that boss there may be journalled a shaft 35 on. which is secured a gear 36 engaged by the worm; there may also be secured on that shaft another gear 37 which peripherally engages a gear 38 secured on the wheel shaft 31. It will readily be understood that rotation of the shaft 32 will be transmitted, in stepped-down angular velocity, to the traction wheel through the secession formed by worm 34, gear 36, gear 37 and gear 38.

Rotation of the shaft 32, and thus rotation of the traction wheel and'propulsion of the carriage, may be accomplished by a driving motor 40. Conveniently this may be mounted, with its main shaft horizontal, at the top of the carriage member 13 from which it may extend toward the axis of the wheel mount 20, and above that mount the motor may be provided with a gear box 41 from which there emerges a driving shaft 42 aligned with that axis. Coupling between the shaft 42 and the shaft 32 may be provided by an intervening vertical shaft 43 keyed to each.

So long as the mount 20 is not-in process of being turned about its axis, and the carriage is therefore being propelled in a straight line, the rate of its propulsion as seen anywhere in the carriage system is constant, being uniquely determined by the speed of rotation of the driving motor 40 and the ratios of the gearing intervening between its main shaft and the wheel shaft 31. While the mount is in process of being turned about its axis, however, the rate of carriage propulsion as seen at the point of contact of wheel 30 with surface S will be temporarily increased or decreased (depending on the direction of the turn); it is nevertheless desirable for many purposes that the rate of carriage propulsion as seen at the axis of the mount 20 (and thus at any other point fixed within the carriage) still remain constant. This desideratum may be achieved by a suitably determined small offset of the plane of the traction wheel 30 from the axis of the mount 20, as fully described in US. Patent No. 2,461,585 issued, on application of Nelson E. Anderson, to the assignee of the present invention; such an offset is contemplated herein and a typical one has been illustrated in FIGURE 5.

In order to scan the elongated indicium L and thus to derive the intelligence for steering of the carriage-so that the path of its movement over the surface S will correspond to the indicium, the carriage may incorporate an optico-electric system comprising photoelectric means and a lens for projecting an image of a longitudinal segment of the indicium onto that means. At least the photoelectric means-and permissibly the entire optico-electric systemis made angularly movable about-an axis normal to the surface S and thus parallel to the axis of the mount 20. In the illustrated embodiment the optico-electric system, designated generally as 60, is supported within a mount in the form of a vertical barrel 50 which (as better seen in the enlarged cross-sectional FIGURE 3) is journalled in the platforms 11 and 12. More specifically, the barrel 50 at its lower portion may havev clamped thereto one of the races of a ball bearing 53 of which the other race is clamped in the platform 11, while its upper portion may have secured thereto one of. the races of a ball bearing 54 of which the other race is clamped in the platform 12. V

Angular movements of the barrel 50 and of the mount 20 about their respective vertical axes are effected simultaneously and in equal direction, rate anddegree. To effect these movements there is employed a servo motor 110, conveniently having a vertical main shaft; at its lower end this servo motor may rest on and be mechanically coupled into a reducing-gear box 46, at the bottom of which a flange 47 extends outwardly and may be supported above and with a small spacing from the platform 11. Downwardly from the gear box 46, for example near its left rear corner, there may extend a short output shaft carrying a relatively small diameter gear 48; this gear may engage relatively larger-diameter and mutually similar gears 22 and 52 respectively secured on the wheel mount 20 and the barrel 50 slightly above the platform 11, and will impart to those gears, in greatly reduced speed and amplitude, the angular motion engaged in by the shaft of the servo motor. The servo motor 110 is controlled, through electric circuitry by the photoelectric means comprised in the optico-electric system, of which system the preferred construction may now be described.

In connection with the description of the optico-electric system it should be noted that by reason of the gearing 48-22-52 the relationship of the angular positions of the wheel mount 20 and the barrel 50 to each other is uniquely predetermined. FIGURE 4 is frontally viewed cross section of the mount 20 in a particular angular positioni.e., that arbitrarily assumed in the illustration of FIGURES 2- and 3-and it is helpful to observe that FIGURE 3, which shows the optico-electric system in detail and to which reference is now made, is a frontally viewed cross section of the system in the angular position it will occupy while the mount 20 occupies the angular position of FIGURE 4.

The bottom of the barrel 50 is closed by a disk 50 in the center of which is mounted a lens 65 by means of which lens an image of a small area of the surface S may be formed upon a light-sensitive portion of a photoelectric sensing means 154. The means 154 may be of any form whose electrical state is varied by incident light. For example, it may comprise a light sensitive resistor, i.e., a device whose resistance decreases to a degree dependent on the light incident on a light sensitive area of the resistor, which area may for example be a surface formed of such material as cadmium sulfide or cadmium selenide. Mechanically, the resistormay be in the form of a small cylinder in one end of which the light-sensitive area is disposed. The dimensions of the optical system S, 65, 154, are such as to place the lens 65 at a distance from the surface S somewhat greater than the focal length of the lens.

The light-sensitive element 154 is mounted in a carr'iage 156 slidably supported upon a rod 158 extending across a diameter of the barrel 50. A lead screw 160 threadedly engages the carriage 156 for adjustably positioning the carriage along the rod .158 so that the area imaged by the lens 65 can be moved relatively to the projection of the vertical axis V of the barrel 50 upon the surface S in order to adjust the lead A of the tracing device. A motor 162 is provided for driving the lead screw 160 for use in automatically adjusting the position of the carriage with respect to the rod 158' in order to provide the optimum lead.

For the scanning of a line indicium the photoelectric means 154 comprises two light-modulated resistors 71 and 72 (FIGURE 6), preferably peripherally continguous to each other with light-sensitive areas 71a and 72a, respectively.

By the lens 65 there will be projected onto the plane of the light-sensitive areas 71a and 72a an image of the indicium which appears on the surface S. The lengthwise direction of the image is such as to render the line between the centers of the areas, and thus their mutually aligned major dimensions, transverse to the image; FIG- URE 6 illustrates as I a shaded strip representing that image for the case of the line indicium L of FIGURE 1. Positioning of the plane of 71a and72a to result in the desirable accurate focussing of the image at that plane may be provided in known manner. Advantageously, the width of the line indicium and the degree of magnification of the image relative to the line are so chosen that the width of the image will be of the same order ofmagnitude as the major dimension of either of the areas 71a and 72a and preferably is substantially the same. As will hereinafter appear, the normal lateral relationship of the image relative to those rectangles is one of equal partial overlaps; in view of the typical dimensioning mentioned above, the extent to which the image will marginally overlie each of the areas may be of the order of one-third of the area (as for example about one fourth of the whole cell diameter).

FIGURE 6 also illustrates a third photoelectric device 73 having a light sensitive area 73a, which is utilized in tracing an edge as discussed and shown in FIG. 10 of the above-mentioned Purkhiser patent. A detailed discussion of the edge tracing operation will not be made in view of the disclosure in the Purkhiser patent.

Illumination of the portion of the indicium of which the image is projected by the lens 65 may be provided in any convenient manner. By way of example FIGURE 3 illustrates an electric bulb 5 contained in a suitable housing 7; the housing may be carried at the lower end of an adjustable goose-neck 8 secured at its upper end of the platform, and may be provided with a suitable condensing lens 6 for the concentration of a substantial portion of its light output on the surface S underneath the lower end of the optico-electric system.

In order to make electrical connections from stationary circuitry to the terminals of the light sensitive resistors, which are contained in the angularly movable barrel 50, that barrel may be provided at its top with a cylindrical upward extension 49 of insulating material in the surface of which (see FIGURE 3) are inset a plurality of parallel spaced slip rings 77 respectively connected to the cell terminals. Electrical connections to these slip rings and thus to the resistor terminals may be made by spaced spring contact fingers 78 which are se cured to a suitable insulating block (not shown) on top of the platform 12 and from that block extend into contact with the respective slip rings.

The electric circuitry, represented schematically by a broken line 111 in FIGURE 3, by which the light-sensitive resistors 71 and 72 control the servo motor may be of any suitable form, a preferred example of which will be found in the above cited Purkhiser patent, and, not being a part of the present invention, is not shown in detail herein.

In brief, the control system of Purkhiser operates as follows. Let it be assumed that the carriage is in the position illustrated in FIGURES l, 2 and 3 and moving along the line indicium L in a leftward direction, that the axis of the optico-electric system intersects the indicium midway between the edges of the latter, and that the lens 65 is therefore projecting onto the plane of the sensitive areas 71a and 72a the dark image I of the indicium in the laterally centered position illustrated in FIGURE 6, under these conditions the fractions of the respective areas 71a and 72a covered by the dark image are equal (and the lighted fractions of those areas are equal and therefore the resistances of 71 and 72 at least nearly equal). A balancing potentiometer (not shown) will previously have been adjusted so that under these conditions there will be zero voltage drop across the potentiometer and there will be no rotation of the servo motor 110.

This state of affairs will continue as the carriage movement continues so long as there is no departure of that axis from the center of the line indicium. If and when a departure begins, one of the areas 71a and 72a will become slightly less covered and the other slightly more covered by the image; the resistance of one of the resistors 71 and 72 will decrease and that of the other will increase; and A.C. voltage of magnitude depending on the degree of the departure, and of one or the opposite phase according to the direction of the departure, will appear across the potentiometer steering the moving carriage (through gear 22) so as to bring the axis of the optico-electric system back to the lateral center of the indicium. Thus each incipient departure occasions an action which annuls that departure; the net result is that the movement of the carriage takes place with the axis of the optico-electric system strongly constrained to remain aligned with the lateral center of the line indicium, therefore takes place in a path corresponding extremely closely with that indicium-Whatever the corners, curves or other deviations from rectilinearity may characterize that indicium.

It will also be appreciated that concomitantly with the steering, or control of the direction of propulsion, of the carriage there will be exerted (through gear 52) a control of the angular position of the barrel 50 and thus of the pair of light-modulated resistors 71 and 72 (considered as a pair), the result of which is to maintain the mutually aligned major dimensions of the areas 71a and 72a at right angles to the indicium L and its image I so that relative thereto those areas remain in the orientation which makes possible the continuing action described in the preceding paragraph.

For stability of behaviour of the apparatus and for fidelity of tracing, as above noted, it is important that the point of intersection of the axis of the optico-electric system with the line indicium (and thus with the surface S) be very slightly displaced forwardly (i.e., in the direction of carriage movement) from the point at which the surface S is intersected by the vertical axis of rotation of the barrel 50. This displacement A constitutes the lead distance in this embodiment of the invention. If the magnification ratio of the optical system is one to one, then the displacement of the photocells from the vertical axis of rotation of the barrel 50 is the same as the lead distance measured in the surface S. Otherwise, the displacement of the photocells from the vertical axis is different from the lead distance measured in the surface S and is equal to the lead distance A multiplied by the magnification ratio R, as indicated at RA in FIGURE 3.

It will be evident to those skilled in the art that the positions of the lamp and the light sensor may be interchanged with similar over-all results. Whereas in the arrangement shown herein the lamp provides general illumination over a large area of the template including a portion of the line to be traced, the lamp may instead be mounted upon the carriage 156 and may be arranged so as to provide a restricted pencil of light which illuminates a small area of the template and which will fall upon the line to be traced or will depart therefrom as the tracing operation proceeds. The light sensor in this case is placed where it receives general illumination from the template which varies accordingly as the pencil of light falls upon the line or departs therefrom.

For the purpose of effecting automatic control of the amount of lead, a servo 164 is provided. The servo acts in response to information as to the speed of the motor 40 to select an optimum value of lead for the given cutting speed as determined by the speed of the motor 40. The motor 162 when in motion operates an odometer 166 that serves to indicate the position of the carriage 156 along the rod 158 and lead screw 160. The motor 162 is started, stopped, and reversed in direction when necessary by means of a suitable control indicated diagrammatically at 168. The motor 40 is provided with suitable speed selecting means 170 which can be adjusted manually by means shown as a knob 172. Electrical or mechanical data defining the position of the knob 172 is conveyed to the servo 164 by suitable means represented schematically by a broken line 174, while other electrical or mechanical data defiining the reading of the odometer 166 is conveyed to the servo by other suitabe means represented schematically by a broken line 176. An electrical or mechanical output from the servo 164 is conveyed to the motor control device 168 by a suitable means represented schematically by a broken line 178,

The operation of the automatic control elfected by the servo 164 is to obtain and maintain a desired relationship between'the speed of the motor 40 as set by means of the knob 172 and the position of the carriage 156 upon the rod 158, the relationship being such as to provide the optimum lead at any given speed of the motor 40.

FIGURE 7 shows a modification of a portion of the structure and circuitry of FIGURE 3 to accommodate a magnetic type of line sensing device instead of the optical type shown in FIGURE 3. The mechanical arrangement for adjusting the lead and the control arrangements for causing the amount of lead to be varied as a function of the travel speed of the tracing device are substantially the same as shown in FIGURE 3, only enough of these arrangements being duplicated in FIG- URE 7 to show how the modified sensing device is connected into the control system. The barrel 50 may be used with a bottom plate a rod 158, and a lead screw supported by the barrel. A modified carriage 156' will be provided with a suitable bore 200 for slidably accommodating a lever 202, the lever performing the magnification function of the ray of light 157 in FIGURE 3. The sensing device is shown as a magnet coil 204 suitably mounted at the lower end of the lever 202. Electrical output leads from the coil 204 are shown at 206 and may be contacted by means of slip rings as in FIGURE 3, if desired. The leverhas its fulcrum in any suitable joint, illustrated in FIGURE 7 as a bearing 208. When the lead screw 160 is turned, the carriage 156" is moved, turning the lever 202 about its fulcrum and varying the lead of the sensing device 204 along the surface S. The bore 200 is tapered so as to allow the lever 202 to change its angle as the carriage 1'56 moves. The lower opening of thebore 200 is preferably a close fit for the lever 202 by means of which the upper end of the lever is guided accurately while at the same time the lever can slide through the said lower opening to accommodate a varying angle of the lever to the vertical as the carriage is moved. The connections to the motor control 168 and from the odometer 166 are the same as shown in FIGURE 3, and the over-all operation is the same as described in connection with FIGURE 3. The line to be traced is in this instance assumed to be detectable by magnetic scanning.

Alternatively, the servo link between the knob 172 and the lead screw 160 may in certain instances be replaced by a direct mechanical linkage, as by means of'suitable gears and/or cams, etc., between a shaft 171 for the knob 172 and the lead screw 160. In this manner, each setting of the knob 172 may be made to correspond to a defiinite position of the carriage 156- or 156' along the length of the lead screw 160.

The invention has been disclosed as used in a tracer which may trace an indicium of any configuration, in which the carriage is steered by angular control, and which provides not only for steering of the carriage but also for control of the angular position of the scanning means within the carriage. Various aspects of the invention, however, may be useful in connection with a tracer which is to be used only for the tracing of a substantially rectilinear indicium, with a tracer which (for example, by reason of substantial rectilinearity of the indicium) does not provide for control of the angular position of the photoelectric means within the carriage. An example of such an alternative tracer might be one for the guidance of a welding head along an elongated seam relative to which the carriage is steered by lateral movement.

The description has referred to a line in the form of a narrow strip of one luminosity, typically low, physically present on a background of a different luminosity, typically high; it will be understood, however, that the line may be a virtual one only, created for example by an elongated shadow, so long as its image as projected by the lens appears to the photoelectric means as similar to the projected image of a real line.

While illustrative forms of apparatus and methods in accordance with the invention have been described and shown herein, it Will be understood that numerous changes may be made without departing from the general principles and scope of the invention.

What is claimed is:

1. In apparatus for the tracing of an elongated indicium, in combination, an optical sensing device, an optical system including a lens for scanning a surface containing aline to be traced and for forming an image of an area of said surface upon a sensitive portion of said sensing device, said optical system having an optical axis, means to adjust the position of said sensing device relatively to said optical axis in order to scan an area on said surface to be scanned which area is offset from the projection of said optical axis upon said surface to be scanned, means to move said optical system and said sensing device as a unit relatively to said surface to be scanned so as to trace said indicium, means to set the speed of said relative motion, and a servo link connecting said position adjusting mean-s of said sensing device and said speed setting means in order to vary the distance of said sensing device from said optical axis as a function of the setting of said speed setting means.

2. In apparatus for the tracing of an elongated indicium, in combination, a magnetic sensing device, a mechanical system including a lever and a fulcrum, said lever carrying said sensing device at one end thereof in proximity to a surface containing an indicium to be traced, said indicium being distinguishable by means of a magnetic field produced by said sensing device, means to adjust the other end of said lever beyond said fulcrum with respect to a vertical axis through said fulcrum, means to move said mechanical system and said sensing device as a unit relatively to said surface to be scanned so as to cause said sensing device to trace said indicium, means to set the speed of said relative motion, and a servo link connecting said position adjusting means of said sensing device and said speed setting means in order to vary the distance of said sensing device from said Vertical axis as a function of the setting of the said speed setting means.

References Cited UNITED STATES PATENTS 2,992,375 7/1961 Mustonen et a1. 318-31 3,017,552 1/1962 Brouwer 318-62 3,135,904 6/1964 Purkhiser 318-31 3,037,888 6/1962 Lobosco et a1.

B. DOBEK, Primary Examiner US. 01. X.R 31s 30, 31 

